Effect of loading and pyrolysis of carbon-supported cobalt phthalocyanine on the electrocatalytic reduction of CO2.

• Cobalt phthalocyanine (CoPC) is dispersed on carbon black with different methods. • The dispersed materials are pyrolyzed under argon at various temperatures up to 900 °C. • CO faradaic efficiency remained > 45 % post-pyrolysis when catalyst loading > 7.9 wt%. • Spectroscopy (EXAFS) shows that the nature of the pyrolyzed material depends on CoPC loading. • Precursor crystallinity is a critical factor in the reactivity after pyrolysis. Understanding the structure-activity relationship of materials that are active for the CO 2 electrochemical reduction reaction (CO 2 ERR) is crucial for developing stable, high-performance catalysts. In this research, it is first shown that ball-milling is a highly efficient way to disperse cobalt phthalocyanine (CoPC) onto carbon black without influencing the CO 2 electroreduction performance of the resulting materials. Then, the link between the loadings of the CoPC precursor on the carbon support and the CO 2 ERR activity of the pyrolyzed materials is demonstrated. With CO current efficiencies higher than 45% and CO current densities as high as -20 mA cm−2 at -0.77 V vs. RHE, the materials with CoPC loadings of 7.9 wt% and higher were still surprisingly active after pyrolysis at 800 and 900 °C. On the other hand, the CO 2 ERR activity of the materials containing less than 6.1 wt% CoPC was drastically reduced after pyrolysis at these temperatures, with CO current efficiencies lower than 10 %. X-ray powder diffraction revealed that only the materials containing crystalline CoPC before pyrolysis showed good CO 2 ERR activity after pyrolysis at 800 and 900 °C. Furthermore, X-ray absorption spectroscopy showed that the loading of the CoPC precursor influenced the structure of the active sites in the pyrolyzed CoPC/C materials. Overall, this study highlights the importance of the dispersion of CoPC when forming a material that is catalytically active for CO 2 ERR after pyrolysis. [ABSTRACT FROM AUTHOR]